Issue
so first of all i could not think of a better title for this question so i'm open for changes.
I am trying to validate a bean using the bean validation mechanism (JSR-380) with spring boot.
So i got a controller like this:
@Controller
@RequestMapping("/users")
class UserController {
@PostMapping
fun createUser(@Valid user: User, bindingResult: BindingResult): ModelAndView {
return ModelAndView("someview", "user", user)
}
}
with this being the User class written in kotlin:
data class User(
@field:NotEmpty
var roles: MutableSet<@NotNull Role> = HashSet()
)
and this being the test:
@Test
internal fun shouldNotCreateNewTestWithInvalidParams() {
mockMvc.perform(post("/users")
.param("roles", "invalid role"))
.andExpect(model().attributeHasFieldErrors("user", "roles[]"))
}
Invalid Roles are mapped to null.
As you can see i want roles
to contain at least one item with none of the items being null.
However when testing the above code no binding errors are reported if roles
contains null values. It does report an error if the set is empty though.
I was thinking that this might be an issue with how kotlin code compiles as the same code works just fine when the User class is written in java. Like this:
@Data // just lombok...
public class User {
@NotEmpty
private Set<@NotNull Role> roles = new HashSet<>();
}
Same Controller, same test.
After checking the bytecode i noticed that the kotlin version is not including the nested @NotNull
annotation (see below).
Java:
private Ljava/util/Set; roles
@Ljavax/validation/constraints/NotEmpty;()
@Ljavax/validation/constraints/NotNull;() : FIELD, 0;
@Ljavax/validation/constraints/NotEmpty;() : FIELD, null
Kotlin:
private Ljava/util/Set; roles
@Ljavax/validation/constraints/NotEmpty;()
@Lorg/jetbrains/annotations/NotNull;() // added because roles is not nullable in kotlin. this does not affect validation
Now the question is why?
Here's a sample project in case you want to try some stuff.
Solution
Answer (Kotlin 1.3.70)
Make sure to compile the kotlin code with jvm target 1.8 or greater and enable this feature by providing the -Xemit-jvm-type-annotations
when compiling.
For Spring Boot projects you only have to do the following changes (tested with Spring Boot 2.3.3 and Kotlin 1.4.0):
- In your pom set the following property:
<properties> <java.version>11</java.version> <kotlin.version>1.4.0</kotlin.version> </properties>
- Add
<arg>-Xemit-jvm-type-annotations</arg>
to thekotlin-maven-plugin
:<build> <plugin> <artifactId>kotlin-maven-plugin</artifactId> <groupId>org.jetbrains.kotlin</groupId> <configuration> <args> <arg>-Xjsr305=strict</arg> <arg>-Xemit-jvm-type-annotations</arg> </args> <compilerPlugins> <plugin>spring</plugin> </compilerPlugins> </configuration> <dependencies> <dependency> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-maven-allopen</artifactId> <version>${kotlin.version}</version> </dependency> </dependencies> </plugin> </build>
Workaround (pre Kotlin 1.3.70)
Rafal G. already pointed out that we could use a custom validator as a workaround. So here's some code:
The Annotation:
import javax.validation.Constraint
import javax.validation.Payload
import kotlin.annotation.AnnotationTarget.ANNOTATION_CLASS
import kotlin.annotation.AnnotationTarget.CONSTRUCTOR
import kotlin.annotation.AnnotationTarget.FIELD
import kotlin.annotation.AnnotationTarget.FUNCTION
import kotlin.annotation.AnnotationTarget.TYPE_PARAMETER
import kotlin.annotation.AnnotationTarget.VALUE_PARAMETER
import kotlin.reflect.KClass
@MustBeDocumented
@Constraint(validatedBy = [NoNullElementsValidator::class])
@Target(allowedTargets = [FUNCTION, FIELD, ANNOTATION_CLASS, CONSTRUCTOR, VALUE_PARAMETER, TYPE_PARAMETER])
@Retention(AnnotationRetention.RUNTIME)
annotation class NoNullElements(
val message: String = "must not contain null elements",
val groups: Array<KClass<out Any>> = [],
val payload: Array<KClass<out Payload>> = []
)
The ConstraintValidator:
import javax.validation.ConstraintValidator
import javax.validation.ConstraintValidatorContext
class NoNullElementsValidator : ConstraintValidator<NoNullElements, Collection<Any>> {
override fun isValid(value: Collection<Any>?, context: ConstraintValidatorContext): Boolean {
// null values are valid
if (value == null) {
return true
}
return value.stream().noneMatch { it == null }
}
}
And finally the updated User class:
data class User(
@field:NotEmpty
@field:NoNullElements
var roles: MutableSet<Role> = HashSet()
)
Altough validation works now, the resulting ConstrainViolation is slightly different. For example the elementType
and propertyPath
differs as you can see below.
Java:
Kotlin:
Source is available here: https://github.com/DarkAtra/jsr380-kotlin-issue/tree/workaround
Thanks again for your help Rafal G.
Answered By - Tommy Schmidt
Answer Checked By - Timothy Miller (JavaFixing Admin)